1. Field of the Invention
The present invention relates to an electron-emitting apparatus using an electron-emitting device and an image-forming apparatus.
2. Related Background Art
Conventionally, there are two types of electron-emitting devices, that is, a thermionic cathode electron-emitting device and a cold cathode electron-emitting device. The cold cathode electron-emitting device can be a field emission type (hereinafter referred to as an xe2x80x98FE typexe2x80x99) device, a metal/insulation layer/metal type (hereinafter referred to as a xe2x80x98MIM typexe2x80x99) device, a surface conduction type electron-emitting device, etc.
The surface conduction type electron-emitting device is disclosed by, for example, EP-A1-660357, EP-A1-701265, Okuda et al, xe2x80x9cElectron Trajectory Analysis of Surface Conduction Electron Emitter Displays (SEDs)xe2x80x9d, SID 98 DIGEST, p.185-188, EP-A-0716439, Japanese Patent Application Laid-Open No. 9-265897, No. 10-055745, etc. In addition, to simplify the producing method, a vertical type surface conduction electron-emitting device can be used as disclosed by Japanese Patent Application Laid-Open No. 1-105445, No. 4-137328, and U.S. Pat. No. 5,912,531.
Conventionally, in the above mentioned surface conduction type electron-emitting devices, a gap is normally formed in advance by an energization process referred to as an energization forming in an electroconductive film before emitting an electron.
In some cases, a process referred to as an activation operation in which an organic gas is introduced to a vacuum area for electrification is performed. When the activation operation is performed, a carbon film is formed in the gap formed in the electroconductive film and on a surrounding electroconductive film.
The surface conduction type electron-emitting device handled by the above mentioned process applies a voltage to a electroconductive film, and passes an electric current to the device, thereby emitting an electron from the electron-emitting region.
Conventionally, particularly, for an image-forming apparatus of a display device, etc., a CRT has been replaced with a flat type liquid crystal display device. However, since it is not an emissive type device, there has been the problem that a back light is required. Under such circumstances, an emissive type display device has been requested.
The emissive type display device can be an image-forming apparatus which is obtained as a display device configured by a combination of an electron source containing a number of surface conduction type electron-emitting devices, and a phosphor emitting a visible light by an electron emitted by an electron source.
FIGS. 25A and 25B show common examples of an electron-emitting apparatus using the surface conduction type electron-emitting device.
In FIGS. 25A and 25B, reference numeral 2001 denotes a substrate, reference numeral 2002 and 2003 denote electrodes, reference numeral 2004, 2006, and 2007 respectively denote an electroconductive film, a gap, and an anode electrode provided above the device. FIG. 25B shows a schematical sectional view of the electron-emitting apparatus. FIG. 25A shows a shape of a beam of an electron emitted onto an anode electrode 2007 of the electron-emitting apparatus shown in FIG. 25B.
In the electron-emitting device, an electron tunnels the gap 2006 when a drive voltage Vf is applied between the electrodes 2002 and 2003, a part of the tunneled electron becomes an emission electron Ie and is emitted to the anode electrode 2007, and the remaining tunneled electron becomes a device current If flowing between the electrodes 2002 and 2003. The value expressed by Ie/Ifxc3x97100% is referred to as efficiency (electron emission efficiency).
In the electron-emitting device such as a surface conduction type electron-emitting device which utilizes a tunneling phenomenon between the electroconductive members opposite each other with a space of the order of nanometer, a large amount of If flows, thereby reducing the electron emission efficiency.
On the other hand, when an image-forming apparatus is formed by using the above mentioned electron-emitting device, a phosphor is provided for the anode electrode 2007 to convert an electronic beam into a light, thereby realizing an image-forming apparatus. However, a high-precision display device has been recently demanded. Therefore, it is necessary to obtain a high-precision beam for use in a high-precision display device. Furthermore, required is a necessary amount of electron emission satisfying the display features for a pixel size appropriate for a high-precision display device. Therefore, improving the electron emission efficiency is required.
The present invention has been achieved to solve the above mentioned problems, and aims at providing a high-performance electron-emitting apparatus and image-forming apparatus capable of improving the electron emission efficiency and realizing a high-precision electronic beam radius.
The electron-emitting apparatus according to the present invention to attain the above mentioned objects comprises:
a substrate;
an electron-emitting device including a layer structure comprising: a first electroconductive member provided on a surface of the substrate; an insulation layer provided on the first electroconductive member; and a second electroconductive member provided on the insulation layer;
an anode electrode provided apart from the surface of the substrate;
first voltage application means for applying potential, higher than the potential applied to the first electroconductive member, to the second electroconductive member; and
second voltage application means for applying potential, higher than the potential applied to the second electroconductive member, to the anode electrode, wherein
T1 less than Axc3x97exp [Bxc3x97(Vfxe2x88x92xcfx86wk)/(Vf)]
A=xe2x88x920.50+0.56xc3x97log (T3), B=8.7 
where:
on an end plane of the insulation layer placed substantially parallel to the surface of the substrate, an end portion of the first electroconductive member and an end portion of the second electroconductive member are set opposite each other with a space between;
in a direction of the end portion of the first electroconductive member and the end portion of the second electroconductive member set opposite each other, the second electroconductive film is T1 [nm] long;
the first electroconductive member extending from the surface of the first electroconductive member substantially parallel to the surface of the substrate toward the direction in which the end portion of the first electroconductive member and the end portion of the second electroconductive member are set opposite each other is T3 [nm] long;
the work function of the second electroconductive member is xcfx86wk [eV];
the voltage applied between the first electroconductive member and the second electroconductive member is Vf [V].
To attain the above mentioned objects of the present invention, the image-forming apparatus comprises:
(A) a first substrate provided with a plurality of electron-emitting devices;
(B) a second substrate having an anode electrode and an image-forming member;
(C) first voltage application means for applying a voltage to the electron-emitting device; and
(D) second voltage application means for applying a voltage to the anode electrode, wherein:
the electron-emitting device comprises a layer structure having: a first electroconductive member provided on the surface of the substrate; an insulation layer provided on the first electroconductive member; and a second electroconductive member provided on the insulation layer;
first voltage application means applies potential, higher than the potential applied to the first electroconductive member, to the second electroconductive member;
second voltage application means applies potential, higher than the potential applied to the second electroconductive member, to the anode electrode;
T1 less than Axc3x97exp [Bxc3x97(Vfxe2x88x92xcfx86wk)/(Vf)]
A=xe2x88x920.50+0.56xc3x97log (T3), B=8.7 
where:
on the end plane of the insulation layer placed substantially parallel to the surface of the substrate, the end portion of the first electroconductive member and the end portion of the second electroconductive member are set opposite each other with a space between;
in a direction of the end portion of the first electroconductive member and the end portion of the second electroconductive member set opposite each other, the second electroconductive member is T1 [nm] long;
the first electroconductive member extending from the surface of the first electroconductive member substantially parallel to the surface of the substrate toward the direction in which the end portion of the first electroconductive member and the end portion of the second electroconductive member are set opposite each other is T3 [nm] long;
the work function of the second electroconductive member is xcfx86wk [eV];
the voltage applied between the first electroconductive member and the second electroconductive member is Vf [V].
When the above mentioned conditions are satisfied, the times of scattering of electrons emitted from the electron-emitting device can be reduced, and the smaller scattering electron can be used as a main component. Therefore, the electron emission efficiency can be improved, and the high-precision electronic beam radius can be simultaneously realized.